1. Field of the Invention
This invention relates to an improved manufacturing process for liquid crystal device, more paticular to liquid crystal filling device.
2. Prior Art of the Invention
There are well known many kinds of compact display in which liquid crystals are made of use. In such a device, liquid crystal is charged in the very thin cavity formed between opposed substrates. One of the substrates is made light transmissive and the other is made reflective so that opitical characteristics as seen from the transmissive side can be changed by controlling the electric field applied on the liquid crystal between the substrates. Contiguous to the liquid crystal and on each substrate, a pair of electrodes are formed with the liquid crystal in between. At least one of the electrode is separated into a large number of parts with which the liquid crystal constitutes A4 size display having 400.times.200 picture elements in cooperation with polarizing plate. Liquid crystal displays of this kind have been used broadly in microcomputors, ward processers, televisions and the like in order to cope with demands to make the device thin.
Out of processing steps to manufacture the display, charging step for filling the thin cavity without involving bubbles requires dexterity. Prior art charging steps are carried out as follow. Namely, the pair of substrates is laminated with spacers in between and the periphery of the pair is sealed off by adhesive except for an access to the interior of the thin cavity thus formed between the substrates. Then the access of the substrates are dipped in liquid crystal in a vacuum chamber having been evacuated sufficiently. Thereafter, the pressure in the vacuum chamber is increased to the atomospheric pressure whereupon the liquid crystal is injected into the cavity of about 5 to 10 thick in virtue of capillary effect. There are shortcomings, however, in the above process in respect of the following items.
(i) Workers must have skill and dexterity to carry out the charging process because of high viscosity of liquid crystal, especially of (chiral) smectic which is broadly used in this field.
(ii) It takes substantial time to fill the cavity with liquid crystal, paticularlly when one desires filling of a very thin cavity less than 4 micron thick such as ferroelectric liquid crystal (FLC) forming memory media of 0.5 to 3 micron.
(iii) Because of high temperature during the filling process (for instance, it takes 8 to 10 hours at 120.degree. C. to charge FLC to the cavity of A4 size), the sealing structure is likely to be degraded and enter into liquid crystal as an impuruty.
(iv) The spacers tend to move during injection of the liquid crystal and flock apart from the access.
(v) It is wastful that a large part (approx. 90%) of the expensive liquid remains uncharged out of the cavity in vain.